1. Field of the Invention
The present invention relates generally to backlit displays, such as liquid crystal displays (LCD) displays, and particularly to configurations of backlight displays using an asymmetric diffuser, such as an elliptical diffuser.
2. Description of the Related Art
For current flat panel displays such as LCD, edge-lit backlight panels are widely used to provide illumination. Such configurations reduce the thickness of the displays. An example backlight panel may comprise a plate made of optically transmissive material. A linear light source such as a fluorescent tube or a linear array of light emitting diodes (LED) may be disposed at an edge of the backlight panel to inject light into the panel. This light is guided within the backlight panel, which may also be referred to herein as a light guide panel. Extractor features on a rear or front surface of the light guide panel may be used to disrupt the propagation of the light within the light guide panel and cause the light to be ejected from the front surface of the panel toward the LCD.
One or more optical films or sheets of material such as brightness enhancement films (BEFs) may be used to control the angular distribution of light extracted from the light guide panel to the LCD. BEFs, for example, comprise a periodic array of prismatic structures disposed on the surfaces thereof that redirect or collimate the light from the light guide panel along a viewing axis of an LCD (i.e., an axis typically normal to the display). The BEFs bend light toward a more normal angle via direct refraction of incident light. The BEFs may also recycle light outside a desired range of angles. Such light is total internally reflected backward instead of proceeding toward the LCD. This backward reflected light is reflected again toward the BEF at a different angle. This process, referred to as recycling, may be repeated until the light passes through the BEF to the LCD within a desired range of angles. Typically, two orthogonal brightness enhancement films are applied such that the range of distribution of the output light on vertical and horizontal directions is nearly symmetrical.
The superimposition of the periodic structure of the brightness enhancement film and the pixel structure of the LCD may create observable interference fringes, known as a Moiré pattern. This Moiré pattern destroys the uniformity of the backlighting and degrades the display quality. To reduce and/or eliminate the Moiré effect, a diffuser may be disposed between the brightness enhancement film(s) and the LCD to smear periodicity in the light distribution output from the brightness enhancement film(s). In order to eliminate the Moiré effect, the haze value of the diffuser is generally relatively high.
Although such configurations provide satisfactory performance, other designs, which may yield performance enhancements, simplify manufacturing, and/or reduce cost, may be desirable.